The present invention relates to a shaft sealing assembly. More specifically, the present invention pertains to a shaft sealing assembly that prevents fluid such as refrigerant and lubricant from leaking from a compressor.
A typical shaft sealing assembly 50 is structured as follows. As shown in FIGS. 4 and 4A, the sealing assembly 50 is located between a drive shaft 61 and a compressor housing to prevent leakage of fluid from the inside to the outside of the compressor. A first lip ring 51, which is made of synthetic rubber, includes a lip 51a. The lip 51a is formed at the radially inner area of the first lip ring 51. A retainer ring 52, which is made of metal, retains the position of the lip 51a to contact a drive shaft 61. A second lip ring 53, which is made of fluororesin, includes a lip 53a. The lip 53a is formed at the radially inner area of the second lip ring 53 and is curved toward the inside of the compressor (right side in FIG. 4). A spiral pump slit 53b is formed in the lip 53a about the axis of the second lip ring 53. A third lip ring 54, which is made of synthetic rubber, includes a lip 54a. The first lip ring 51, the retainer ring 52, the second lip ring 53, and the third lip ring 54 are arranged in this order from the inside to the outside of the compressor as shown in FIG. 4.
The rings 51-54 are tightly held together in a cylindrical case 55. Accordingly, the first and the second lip rings 52, 53 contact the retainer ring 52 and the case 55.
When the drive shaft 61 is rotating, or when the compressor is operating, high pressure gas in the compressor is applied to the lip 53a of the second lip ring 53. Accordingly, the lip 53a is pressed against the drive shaft 61 by a predetermined force, which prevents leakage of fluid from the compressor. In this state, the pump slit 53b of the lip 53a has a spiral pumping effect and positively sends fluid back between the lip 53a and the drive shaft 16. This also improves the fluid-sealing performance of the second lip ring 53.
When the drive shaft 61 is not rotating, or when the compressor is not operating, the lip 51a of the first lip ring 51 resiliently contacts the drive shaft 61. This prevents leakage of fluid from the compressor. When the drive shaft 61 is not rotating, the pressure in the compressor is relatively low and the lip 53a of the second lip ring 53 is pressed against the rotational shaft 61 by a relatively small force. Accordingly, the shaft sealing assembly includes the first lip ring 51 to compensate for the weak sealing ability of the second lip ring 51.
When the drive shaft 61 is rotating, the lip 51a of the first lip ring 51 allows fluid in the compressor to flow toward the second lip ring 53. The position of the lip 51a with respect to the drive shaft 61 is retained by the retainer ring 52 when high pressure is applied to the inside of the first lip ring 51.
The fluid (mainly lubricant) that leaks by the lip 51a of the first lip ring 51 lubricates and cools the lips 51a, 53a of the first and second lip rings 51, 53. Accordingly, the lips 51a, 53a are not worn by friction. This extends the life of the first and second lip rings 51, 53.
The lip 54a of the third lip ring 54 resiliently contacts the drive shaft 61 and prevents foreign particles from entering. Accordingly, foreign particles do not enter between the lip 53a and the drive shaft 61, which prevents the performance of the second lip ring 53 from deteriorating. When the rotation of the drive shaft 61 is stopped, the third lip ring 54 prevents leakage of fluid that remains between the first lip ring 51 and the second lip ring 53.
However, the first lip ring 51 permits leakage of fluid (refrigerant gas) during the rotation of the drive shaft 61. The seal formed between the second lip ring 53 and the retainer ring 52 and between the second lip ring 53 and the case 55 has a lower sealing performance compared to the contact area seal formed between the first lip ring 51 and the retainer ring 52 and between the first lip ring 51 and the case 55. Accordingly, as shown by FIG. 4A, the refrigerant gas that leaks past the first lip ring 51 is likely to enter between the second lip ring 53 and the retainer ring and between the second lip ring 53 and the case 55.
When the rotation of the drive shaft 61 is stopped, the third lip ring 54 prevents leakage of the fluid remaining between the first lip ring 51 and the second lip ring 53. In other words, the fluid (especially refrigerant gas) between the second lip ring 53 and the retainer ring 52 and between the second lip ring 53 and the case 55 does not flow out of the compressor after the drive shaft 61 is stopped. When the drive shaft 61 is stopped for a relatively long period, the refrigerant gas between the second lip ring 53 and the retainer ring 52 and between the second lip ring 53 and the case 55 can be liquefied by cooler temperatures.
If the drive shaft 61 rotates in this state, the temperature around the shaft sealing assembly 50 increases. Then, the liquidized refrigerant between the second lip ring 53 and the case 55 vaporizes, which moves the second lip ring 53 radially inward. This may release the second lip ring 53 from the case 55. Since the second lip ring 53 and the retainer ring 52 are held together in the case 55 by friction and compression, the release of the second lip ring 53 also releases the retainer ring 52 from the case 55. Accordingly, the retainer ring 52 cannot retain the initial position of the lip 51a of the first lip ring 51 with respect to the drive shaft 61. As a result, the first lip ring 51 may not leak fluid, which causes the first and the second lip rings 51, 53 to wear prematurely.
On the other hand, the released second lip ring 53 may lift the first lip ring 51, through the retainer ring 52, from the drive shaft 61. Thus, when the drive shaft 61 rotates, the first lip ring 51 may leak too much fluid that for the second lip ring 53 and the third lip ring 54 to stop.